The present invention relates to a photothermographic element in which the image that is developed on thermal processing is detected by fluorescence. The photothermographic element comprises a light-sensitive, thermally developable silver image and both a fluorescent material (a fluorophore), the fluorescence intensity of which is modulated as a function of exposure, and a coupling agent that provides an imagewise reaction product, preferably a dye that absorbs part or all of the light that is either absorbed or emitted by the fluorophore.
In conventional photography, an image is recorded on a photographic film, and the film is then processed by immersion in a sequence of processing solutions to provide a record of the light intensities in the original scene as modulations of the concentration of a colored material in the film structure. In the case of a black and white image, the record is usually of the overall intensity of visible light, and the colored material is typically metallic silver formed by imagewise development. Typically in a full-color process, the record is, separately, of the red-, green-, and blue-light information in the original scene, recorded in variations in the concentration of cyan, magenta, and yellow dyes in the film. The image information so recorded is then either viewed directly (as in a slide for projection), or used to print a second image for viewing (as in the production of a print from a photographic negative).
One of the limitations of conventional photography is color correction. In the case of a slide image, no corrections for color rendition, minimum density, image contrast, or the like are possible once the processing is done, the image is essentially viewed directly. Even in the case of the color print, only certain kinds of corrections for improving image quality can be achieved, with difficulty, by manipulation of the color chemistry of the film or the print or by adjusting the printing parameters (exposure, color balance, etc.).
Another limitation of conventional photography is volume of chemicals consumed during processing, posing problems in transport, handling, and disposal. It is always desirable to limit the amount of solvent or processing chemicals used in the processing of silver-halide films. As indicated above, a traditional photographic processing scheme for color film involves development, fixing and bleaching, and washing, each step typically involving immersion in a tank holding the necessary chemical solution.
By the use of a photothermographic film, it would be possible to eliminate processing solutions altogether, or alternatively, to minimize the amount of processing solutions and the complex chemicals contained therein. A photothermographic (PTG) film by definition is a film that requires energy, typically heat, to effectuate development. A dry photothermographic film requires only heat. In some embodiments, a solution-miniunized photothermographic film may require small amounts of aqueous alkaline solution to effectuate development, which amounts may be only that required to swell the film without excess solution. However, completely dry photothermographic processes are generally preferred.
Photothermographic film has typically been scanned, offering the opportunity for enhanced color correction. Acquisition of image information by electronic scanning and digitization is a routine feature of modern imaging technology. If the captured image is first digitized, a much wider range of image modifications are possible by computer manipulation of the image file. At the same time, visually satisfactory images can be constructed from digital information recorded from images on film that would be inadequate for normal viewing or printing. In photothermographic films, since the silver is retained, film images have high minimum optical densities (Dmin). These images can be readily digitized, and manipulated to yield more attractive prints than would be possible using conventional optical printing.
In addition to color correction, another advantage of scanning is that, while in conventional color photography, the image dyes that record the color records are invariably cyan, magenta and yellow, dyes of a much wider range of colors are usable with a suitable scanner. They can be false-colored, for example, so that the red light information is recorded in density of an IR absorbing dye. It is even possible that the dyes corresponding to two different color records can have absorption spectra that overlap substantially, or be sensitized in such a way that there is some mixing of the RGB information in the scene as it is recorded on the film. Algebraic manipulation of the digitized image can be used to compensate in large part for this overlap or the color mixing, so that the true red, green, and blue (RGB) light levels in the original scene can be reconstructed even from these partially convoluted data.
Most digitization schemes involve the same kind of information that is normally used in conventional processing, namely the modulation of a transmitted light beam by light absorption by the dyes incorporated imagewise into the developed image. However, digitization allows completely new ways of gathering the data necessary for reconstructing a visually satisfying image. Various schemes have been proposed. For example, partially reflective, absorbing, or reflective interlayers can aid in the isolation of color records that are all imaged in the same hue (for example, in a silver gray-scale). This kind of image recording scheme has been proposed, for example, in U.S. Pat. Nos. 5,334,469, 5,350,651, 5,350,664, 5,389,503 and 5,418,119. Another approach to the same goal is to use fluorescent interlayers; this method has been proposed in U.S. Pat. No. 5,350,650 and EP 0 702 483 A2.
Another way of recording images has been disclosed by Schumann et al., in U.S. Pat. No. 4,543,308, who used fluorescence from retained sensitising dye to record imagewise information from a number of color film and paper formats. Schumann et al. noted certain advantages of a fluorescent imaging scheme over an imaging system based on dye absorption. For example, detection of fluorescence can be done at extremely low levels, so that only very small amounts of fluorophore would be necessary for imaging. The fluorophore could take the place of much larger quantities of expensive dye-forming couplers in the conventional approach, so that the film would be less expensive to manufacture. Further, the small amounts of imaging fluorophore would allow coating of substantially thinner film structures, with possible improvements in image structure and manufacturing economy. However, the elements of Schumann et al. are all processed by conventional means and do not involve images generated by thermal development.
Schumann et al. state that dye-forming couplers are unnecessary for fluorescent imaging, although they apparently have no adverse effect if they are used. The use of couplers, however, would undermine the main advantages of his invention, that is, the replacement of expensive couplers by much smaller amounts of fluorescent dyes and the subsequent ability to make thinner imaging layers. For comparison, in Example 7, Schumann et al. disclose the use of couplers, although they employ silver removal when forming colored dyes from couplers. Thus, certain disadvantages, but no apparent benefits, are mentioned from the use of couplers in the fluorescent imaging system of Schumann et al.
In view of above, all of the cases in which fluorescent imaging has been used for recording image information have involved wet chemical means to develop and/or produce an image to modulate the fluorescence, by light absorption either by silver or by developed dye. Fluorescence imaging in a thermally processed film has not previously been accomplished. Such an imaging scheme would require that fluorescent materials be sufficiently compatible with the high temperature processing conditions and the chemical components uniquely present in photothermographic elements. The fluorescent materials (xe2x80x9cfluorophoresxe2x80x9d) would need to be capable of withstanding high temperatures in the presence of the complex set of chemicals necessary to cause silver development in a photothermographic element, even though fluorophores tend to be large, sensitive, and reactive entities. Chemical components present in photothermographic elements, but not present in conventional systems, may include, for example, organic silver salts, melt formers, and blocked developers or other compounds that generate reactive intermediates during thermal development. It has never been determined whether a fluorescent latent image would form or would be detectable in a photothermographic element, rather than being quenched or obscured by the above-mentioned chemicals components or by other film constituents that might interfere, including components such as developing agents in both reduced and oxidized form that would have been washed out in conventional processing.
In U.S. Pat. No. 4,543,308 to Schumann et al., imaging in multilayer color photographic materials used either separation exposures or white light exposures. Furthermore, all of the white light exposures corresponded to bleach-fixed materials. Schumann et al., therefore, did not actually demonstrate that color imaging is possible in conventional film, let alone in film where the cross-talk between unfixed layers is large. In photothermographic film that is unbleached and unfixed, any fluorescence image would need to be viewed in the presence of, and through, the highly scattering and absorbing layers of other colors.
Finally, Schumann et al. taught that most of the fluorescent latent image appears with low levels of silver and silver development. This observation suggests that the fluorescent latent image would likewise be sensitive to low fog levels. Photothermographic elements, especially chromogenic elements, suffer from the presence of substantial fog, which conceivably could adversely effect a fluorescent image scale. Despite the various unknowns and potential problems, achieving fluorescent imaging in a phototothermographic material would be highly desirable.
The advantages of such fluorescent imaging would be especially apt for a photothermographic element, in contrast to conventional film, since according to Schumann et al. no fixing and bleaching are required and since in photothermographic film, no wet development is necessary. Therefore, no wet processing at all would, therefore, be necessary in photothermographic film, as compared to the process taught by Schumann et al. With respect to conventional films, since wet development is required anyway, the absence of fixing and bleaching would not be as advantageous and may even be undesirable for reasons of remediation. In contrast, with respect to photothermographic systems, the absence of wet development would allow the use of kiosks for speedily providing imaged prints to customers using a dry process, while optionally allowing later remediation using wet processing.
Since one of the aims of scanning and digitization is to avoid as much as possible the expense and inconvenience of this complex processing chemistry, together with its environmental and occupational safety risks, it would be advantageous to couple scanning technology with a simpler process, for example a thermal process, in which the exposed film sample is simply heated to produce a silver image suitable for imaging purposes. A substantial amount of work has been carried out to design scannable films using conventional imaging schemes based on light absorption by dyes that require only thermal processing for the development of an image.
In copending concurrently filed, commonly assigned application Ser. No. 10/032870, Applicants have recently described a thermally processable fluorescent imaging element that comprises at least one layer coated on a support, the layer comprising as essential elements a light-sensitive silver halide emulsion, a fluorescent material (a fluorophore), and an incorporated developer. While fluorescent images can be obtained by exposure and thermal processing of this element, the images are not of the highest quality. The contrast of the images produced by these elements (the degree to which variations in exposure are rendered in variations of fluorescence intensity) is relatively low, and the photographic speed (the sensitivity of the element to light) is also low relative to similar elements using the same silver halide emulsions, but processed in aqueous solutions to produce a dye image that can be viewed visually. It would be greatly advantageous for the practical application of this approach to imaging to find ways of improving both the light sensitivity and the photographic response of the fluorescent imaging element.
The present invention describes a photothermographic imaging element comprising at least one silver halide imaging layer containing a fluorescent substance (xe2x80x9cfluorophorexe2x80x9d) and a coupling agent, which imaging element can be exposed and then processed by heating to form an image in which the intensity of the fluorescence from the element is modulated imagewise to yield a fluorescent image of the light intensities to which the element was exposed. The fluorescent image can then be digitized using a suitable digital detecting device, such as a scanner, and digitally processed and printed to yield a visually accessible image of the original data (that is, a photographic image).
The term xe2x80x9cscannerxe2x80x9d as used herein refers to a device for forming image-bearing electronic signals from two-dimensional images, and the term xe2x80x9cscanningxe2x80x9d as used herein refers to the process of translating a photograph film into an electronic form that can be used by computers. Preferably, the scanner is also capable of converting the electronic signals to digital form. In a preferred embodiment, scanners comprise one or two-dimensional CCD array detectors.
A preferred embodiment of the invention is directed to a color photothermographic film having at least three light-sensitive units which have their individual sensitivities in different wavelength regions, each of the units comprising at least one light-sensitive silver-halide emulsion, one or more organic silver salts, and binder, and a developing agent or precursor thereof.
The present invention is also directed to a method of processing photothermographic film that has been imagewise exposed in a camera, which method in order comprises: (a) thermally developing the film step without any externally applied developing agent, comprising heating said film to a temperature greater than 80xc2x0 C. in an substantially dry process; and (b) detecting the luminescence latent image emitted by a fluorescent dye associated with at least one imaging layer (any one or all of the color light-sensitive units in a color film) and, based thereon, providing a digital electronic record capable of generating a positive image in a display element, wherein substantially amounts or all of the silver and silver halide salts in the film are not removed before detection. Thermal activation preferably occurs at temperatures ranging from about 80 to 180xc2x0 C. In one embodiment of the invention, at least initial processing is accomplished in a kiosk.
Applicants have found that the incorporation of the coupling chemistry into the fluorescent imaging element results in dramatically improved fluorescence imaging. This modified fluorescent imaging element can display higher photographic speed, higher contrast, and improved image discrimination.
A preferred embodiment of the invention employs dye-forming chemistry involving the combination of a developing agent that generates an oxidized form on reaction with exposed silver halide, together with a coupler capable of forming a reaction product that is a colored dye, by reaction with the oxidized form of the developer. This kind of chemistry is commonly employed in conventional imaging systems, both those that are thermally processed and those that use conventional wet-chemical means for development.